This Program Project grant submission requests funds to support continued studies of genetically engineered HSV-1 (HSV) as a novel, yet practical approach to the treatment of human brain tumors. The interdisciplinary expertise of investigators at the University of Chicago (Drs. B. Roizman and R. Weichselbaum) and the University of Alabama at Birmingham (Drs. R. Whitley, J. Markert, Y. Gillespie and J. Parker) will continue to generate molecular biologic data on genetically engineered HSV and to translate their observations to Phase I clinical trials of human glioblastoma multiforme. This highly collegial and productive group of investigators began these studies four and a half years ago with three projects and two cores. We now propose four projects and three cores, as the clinical adaptation of our fundamental discoveries becomes more immediate. Roizman proposes to construct entirely novel therapeutic HSV that will specifically target cell surface receptors expressed specifically and at high abundance on glioma cells in situ. Already, they have preliminary constructs that selectively infect and, replicate only in, human glioma cells. Weichselbaum will focus on the synergistic anti-tumor interaction between HSV and radiation therapy. Based upon their fundamental observation that radiation enhances viral replication and spread within intracranial tumors, they propose to identify cellular and viral genes that are up/down regulated so that they can use these data to drive the design of new viruses that exhibit this synergistic effect. Whitley will focus on the generation of viruses with enhanced oncolytic potential for human gliomas. They will determine whether viruses selected with novel properties demonstrate enhanced neurovirulent properties. New viruses and treatment enhancing discoveries will be funneled into Markert, which will begin the process of translating genetically engineered viruses to clinical trials. A genetically engineered deltagamma1 34.5 HSV that expresses Interleukin-12 was constructed during the initial period of funding and will be the first candidate virus to be advanced into Phase I clinical trials. Each of these projects is supported by three cores: Whitley (including biostatistical support), Experimental Animal Glioma Model-Gillespie (testing safety and efficacy in relevant animal models) and Viral Production-Parker (production and characterization of highly purified, high-titered virus stocks). This team of investigators anticipates enhanced successes in the future period of funding.